How to photograph traffic trails and light streaks

Light streaks or traffic trails are when lights moving through a scene leave a light trail. They are easy to do and for a beginner, can be very rewarding.

London Tower Bridge with traffic trails

London Tower Bridge traffic trails – ISO100, 10 seconds @ F/16

Let’s discuss some basic physics before we dive into camera settings and techniques. This background would arm you with some basic knowledge that should help you tackle any situation like this in the future. Of course if you wish, please feel free to skip to the guides further below.

What are light streaks and how do they appear the way they do in a photo?

Light streaks primarily happen when a bright light source moves through a field of view. The light source is not a long consistent object, it is typically from a point source, such as the headlight of a vehicle. So a light streak is like the smearing of the point source as it travels through the view. They are smooth streaks, not many individual points of light through the scene, due to the way the exposure is taken by the camera.

When an exposure is taken, the camera sensor (or film) is constantly gathering light through the length (time) of the exposure. If anything moves in the duration of the exposure, called the shutter speed, then it is moving smoothly. If, for example, a person walks through the scene and they are not reflecting enough light for the sensor to register the photons then they would not appear in the photo (Hint: How to take photos without people in the scene). Or they may appear ghostly/transparent as some of the photons bounced off them and into the sensor whilst the rest of the photons of light from the background added up to make the background they moved through.

The same is happening with a light streak. The light source (headlight) is moving smoothly through the scene constantly emitting photons, a lot of them. Because it is moving smoothly through the scene and emitting a lot of photons, the sensor has constantly gathered the photons throughout the smooth movement of the light source resulting in a streak.

Quick Guide

To get you started quickly try the following.
You would require some prior knowledge on the exposure triangle to follow the method below.

  1. Set the camera on a tripod or a solid surface, as you would be taking a long exposure, and then frame the scene
  2. Set the ISO to 100
  3. Set the camera to manual mode so that you control the Aperture and Shutter Speed. This is “M” Mode on the dial at the top of the camera. If you cannot manually control the camera then set the camera to TV mode or where you can control the shutter speed
  4. Set the shutter speed to 5 seconds – If you are unable to manually set the shutter speed on your camera then taking a light streak image would be very difficult
  5. If you can, set the aperture to properly expose the scene (or let your camera decide this if you are unable to set the aperture)
  6. Start taking photos as traffic passes through the scene

france paris arc de triumph at night

Arc de Triomphe from Champs Elysees – ISO100, 2 seconds @ F/9

Detailed Guide

Step 1 – Artistry

When I take a photo with light streaks, I try and think about the end result and what the light streaks are going to bring to the scene. The end result could be a point of interest, a leading line, a complementary colour or just something abstract.

Sometimes the light streaks are subtle and play a minor role and sometimes the light streaks play a major role. Referring to the photo above of Tower Bridge, the idea there is to use the light streaks as leading lines into the photo. They play a major role in that photo.

Have a reason for including the light streaks and balance the image. Try not to include them just because you can;-)

Step 2 – Framing the Scene

Choosing the camera position could be quite difficult, as it would be dependant on your vision. If you are trying to include the light streaks as leading lines then you would position the camera to enable the light streak to lead into the scene and to your subject matter. This may be the middle of the road. If that is the case then try and find a safe position such as a traffic island.

Try not to frame the scene where the headlights of a vehicle will beam straight into the lens. Your images could wash out and you would lose contrast. Have the traffic pass by at an angle.

If you are head on to the traffic then stop down to F/16 or smaller aperture (bigger F-number). F/16 – F/22 produces a very small aperture opening. This small aperture opening would only allow direct photons of light onto the sensor. Most of the photons of light coming from an angle would hit the aperture blades and only the direct photons would register, which would increase contrast and reduce the washed out (glow) look.

italy rome colosseum light trails

The Colosseum in Rome – ISO100, 15 seconds @ F/16

Step 3 – Timing: Watching the scene for The Gap or The Scene

There are 3 types of traffic movement:

  1. All vehicles are stationary, such as at a red light
  2. Vehicles are starting to move, just after the green light. Some vehicles are stationary
  3. All vehicles are in motion

For point 1, this is what I call The Gap. It is where you have your subject matter framed and the vehicles lights are stationary. Taking this scene would result in a star burst effect, when your aperture is at F/16 or smaller. If you do not have any vehicles framed in the scene then you would receive a clean image.

For point 2, this is the worst time to start the exposure in my opinion. You would have a combination of stationary vehicles, light streaks and star bursts, which can lead to a messy or busy scene. I think you should do one or other. But of course, break the rules! Don’t listen to what I have to say, please go and try it out. I bet you can get a great image.

For point 3, this is what I look for and I call The Scene. All the vehicles are moving which results only in light streaks. The point at WHEN you start the exposure is important. Let’s examine the same composition with two different exposures:

Big Ben at night with traffic trails

Big Ben with Traffic Trails – ISO100, 15 seconds @ F/22

Both of the images were taken with exactly the same settings. The important factor of the exposure triangle is the shutter speed, however, it is WHEN the exposure was started that makes the difference.

The exposure on the left was started when the the traffic lights where changing and the cars started to move. You can see the streaks of light starting and ending in the scene, like short luminous spaghetti strands. This exposure was started at point 2, that I mentioned earlier.

The exposure on the right was started when all of the vehicles were in full flow. The light streaks are long and enter into and out of the scene. This is “The Scene” that I would like to capture.

Step 4 – The Exposure

Taking a light streak/traffic trail scene is the same as taking a long exposure photo. The only difference is when you start the exposure, which we have covered in the previous step and how long you leave the shutter open for.

The duration of the exposure is important because it will determine the length of the light streak. If you would like a light streak to extend through your scene, maybe enter in and out of it, then you should watch the scene first. Track how long it takes for the full flowing traffic to enter your framed scene and exit it. This duration should then be your shutter speed and you would adjust your aperture and ISO accordingly to correctly expose the rest of the scene.

Let’s discuss a light streak that does not involve vehicles.

This is a sequence of events with the London Eye as the subject matter. My vision was to get a single continuous ring of light.

London eye light streak sequence 001

London Eye Light Streak – ISO100, 10 seconds @ F/9

The wheel is obviously rotating very slowly. From this first exposure of 10 seconds, light is starting to streak but not long enough to create a single ring of light. The factor that determines time in the exposure triangle is the shutter speed. I adjusted it to 60 seconds and the aperture to F/22, to stop the sky from blowing out.

London eye light streak sequence 002

London Eye Light Streak – ISO100, 60 seconds @ F/22

Great, I achieved my vision. But you know what is great about photography, experimenting and having fun.

You just never know…

London eye light streak sequence-003

London Eye Light Streak – ISO100, 207 seconds @ F/22

Please refer to my “How to take great photos at night” tutorial to learn more about taking long exposure photography. I also explain the stages involved in taking the above zoomed London Eye image.

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